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Dyax got some good news late today that sent shares booming. The Cambridge, MA-based company (NASDAQ: DYAX) said it has received FDA clearance to start selling a drug that treats hereditary angioedema, a rare genetic condition in which people get rapid attacks of pain and swelling in the face, hands, feet, and lungs.

The company can now start selling ecallantide (Kalbitor) in patients age 16 or older with hereditary angioedema. Dyax has agreed with the FDA to set up a risk evaluation and mitigation strategy, so that doctors can tell the difference between severe symptoms of the disease, and a severe hypersensitivity reaction to the drug known as anaphalaxis that can cause potentially fatal swelling in the airways.

Shares of Dyax climbed 37 percent, to $4.80 in after-hours trading following the announcement.

The approval is significant because it is the first treatment of its kind that can be injected just under the skin. It’s also the first marketed product for Dyax, which has been around since 1995, and has traditionally generated its revenues from licensing proprietary drug discovery technology, known as phage display, to other companies. The company’s application to market its first drug was dealt a regulatory delay by the FDA in March, although the company said then it wasn’t required to do more clinical trials.

It’s hard to say how big the market will be for this drug. Dyax didn’t disclose what the price will be for the new treatment, and a spokeswoman didn’t immediately respond to an e-mailed request for the price, but the patient population for this drug is definitely small. Estimates are that one in 10,000 to one out of 50,000 people suffer from hereditary angioedema, the company says.

“The approval of Kalbitor represents an important milestone in our ongoing commitment to the hereditary angioedema community,” said Gustav Christensen, Dyax’s CEO, in a statement.